Digital media, such as video, is sometimes encoded such that a current portion of the encoded media refers to another portion of the encoded media. As an example of inter-picture coding, parts of a current video picture are sometimes encoded by reference to other video pictures that were previously encoded and decoded. The previously encoded/decoded pictures are termed reference pictures. Thus, decoding the current portion depends (to at least some degree) on information in the other portion.
In some cases, the other portion of the encoded media may be partially or completely unavailable. In such cases, it can be difficult or impossible to accurately decode the current portion. Such a situation can arise, for example, when encoded video is delivered over a network connection, and a user switches between channels of video (examples of channel start operations). Or, such a situation can arise, for example, when a user plays back a video file and moves forward or backward in the video (examples of file seek operations). In these scenarios, dependencies of a current video picture on unavailable reference pictures can result in failure of decoding. This can show up as missing blocks on the screen (“macroblocking”) or other corruptions in one or more displayed pictures.